98 CALCAREOUS MANURES— PRACTICE. 



ing any bulk of crop expected from their use. But one bushel of gypsum 

 spread over an acre of land fit for its action, may add more than twenty 

 times its own weight to a single crop of clover hay. 



But without pretending to account for the wonderful action of gypsum 

 as manure, and without entertaining any confidence in any of the nume- 

 rous theories heretofore presented, (not excepting the latest set forth, by 

 Professor Liebig,) I concur in the general opinion expressed by Davy. 

 This accurate investigator, who took nothing upon trust which could be 

 subjected to the test of rigid experiment, pursued that mode to obtain light 

 on this obscure subject. He found by chemical analysis, that gypsum was 

 always present in the ashes of red clover, and in quantity, in a good crop, 

 amounting to three or four bushels to the acre. He inferred that gypsum, 

 thus always forming a portion of the clover plant, was essential to its healthy 

 existence— and that it is necessary to the structure of the woody fibre of 

 clover and other grasses. But it is enough if Davy was correct in the 

 main opinion, that a certain though very small proportion of gypsum is an 

 essential component part of certain plants, of which the clover tribe fur- 

 nishes the most noted examples. If this be so, no matter what may be the 

 office or function of the gypsum, the small amount necessary for the de- 

 mands of the plants tmist be present in the soil, or otherwise the plants need- 

 ing it cannot live, or maintain a heaUhrj growth. It will follow, further, 

 that on soils well adapted for clover in other respects, but almost totally 

 deficient in gypsum, the application of so small a dressing as one bushel 

 of that substance to the acre may enable a full crop of clover to grow, and 

 twice or thrice as much as the land could have brought without this small 

 application. Such I suppose to be the circumstances of those lands of this 

 country on which gypsum exerts the greatest power. But in England, 

 though clover culture is universally extended, gypsum has shown scarcely 

 any benefit as manure, and though extensively experimented with, has not 

 been found sufficiently oj^erative to be brought into ordinary practice on any 

 one farm in the kingdom. This may be accounted for by supposing the 

 soils generally to be supplied by nature abundantly witli gypsum, so that 

 no more is required. Davy found gypsum in the soil itself of four farms, 

 examined with this view, and in one of them the very large proportion of 

 nearly one per cent. (See Agricultural Chemistry, Lecture vii.) But there 

 is another and numerous class of cases in which gypsum cannot be sup- 

 posed to be present, and yet when applied shows no benefit. These are 

 the poor acid soils of lower Virginia, (and elsewhere,) and the cause of 

 which it seems to me not difficult to explain. 



However wonderful and inscrutable the fertilizing power of this manure 

 may be, and admitting its cause as yet to be Hidden, and entirely beyond 

 our reach— still it is possible to show reasons why gypsum cannot act in 

 many situations, where all experience has proved it to be worthless. If this 

 only can be satisfactorily explained, it will remove much of the uncertainty 

 as to the effects to be expected ; and the farmer may thence learn on wliicli 

 soils he may hope for benefit from this manure —on which it will certainly 

 be thrown away — and by what means the circumstances adverse to its ac- 

 tion may be removed, and its efficacy thereby secured. This is the expla- 

 nation that I shall attempt. 



If the vegetable acid, which I suppose to exist in what I have called acid 

 soils, is not the oxalic, (which is the particular acid in sorrel,) at least every 

 vegetable acid, being composed of different proportions of the same three 

 elements, may easily change to any other, and all to the oxalic acid. This, 

 of all bodies known by chemists, has the strongest attraction for lime, and 

 will take it from any other acid which was before combined with it, and for 



